Olfactory bulb drives respiration-coupled beta oscillations in the rat hippocampus

The synchronization of neuronal oscillations has been suggested as a mechanism to coordinate information flow between distant brain regions. In particular, the olfactory bulb (OB) and the hippocampus (HPC) have been shown to exhibit oscillations in the beta frequency range (10-20 Hz) that are likely to support communication between these structures. Here we further characterize features of beta oscillations in OB and HPC of rats anesthetized with urethane. We find that beta oscillations simultaneously appear in HPC and OB and phase-lock across structures. Moreover, Granger causality analysis reveals that OB beta activity drives HPC beta. The laminar voltage profile of beta in HPC shows the maximum amplitude in the dentate gyrus, spatially coinciding with olfactory inputs to this region. Finally, we also find that the respiratory cycle and respiration-coupled field potential rhythms (1-2 Hz) - but not theta oscillations (3-5 Hz) - modulate beta amplitude in OB and HPC. In all, our results support the hypothesis that beta activity mediates the communication between olfactory and hippocampal circuits in the rodent brain. This article is protected by copyright. All rights reserved.2018-09-2

Functional Convergence of Neurons Generated in the Developing and Adult Hippocampus

The dentate gyrus of the hippocampus contains neural progenitor cells (NPCs) that generate neurons throughout life. Developing neurons of the adult hippocampus have been described in depth. However, little is known about their functional properties as they become fully mature dentate granule cells (DGCs). To compare mature DGCs generated during development and adulthood, NPCs were labeled at both time points using retroviruses expressing different fluorescent proteins. Sequential electrophysiological recordings from neighboring neurons of different ages were carried out to quantitatively study their major synaptic inputs: excitatory projections from the entorhinal cortex and inhibitory afferents from local interneurons. Our results show that DGCs generated in the developing and adult hippocampus display a remarkably similar afferent connectivity with regard to both glutamate and GABA, the major neurotransmitters. We also demonstrate that adult-born neurons can fire action potentials in response to an excitatory drive, exhibiting a firing behavior comparable to that of neurons generated during development. We propose that neurons born in the developing and adult hippocampus constitute a functionally homogeneous neuronal population. These observations are critical to understanding the role of adult neurogenesis in hippocampal function

Rapid triggering of vocalizations following social interactions

SummarySocial interactions are multifaceted, composed of interlinked sensory-motor behaviors. The individual significance of each of these correlated components cannot be established without observing the full behavior. Recently, Wesson [1] concluded that rats display their submissive status by lowering sniff rate following face-to-face encounters with a dominant conspecific. How rats can perceive such changes in sniff rate is unclear. We recorded sniffing and vocal production of rats during social interactions. Face-to-face encounters with a dominant rat immediately elicited 22 kHz alarm calls in the submissive. The large drop in sniff rate observed in submissive rats was caused by the prolonged exhalations needed to produce these calls. We propose that, while submissive rats do lower sniffing rates around face-to-face encounters, dominant rats need not directly perceive this change, but may instead attend to the salient 22 kHz alarm calls

Sequence Determinants of Quaternary Structure in Lumazine Synthase

Riboflavin, an essential cofactor for all organisms, is biosynthesized in plants, fungi and microorganisms. The penultimate step in the pathway is catalyzed by the enzyme lumazine synthase. One of the most distinctive characteristics of this enzyme is that it is found in different species in two different quaternary structures, pentameric and icosahedral, built from practically the same structural monomeric unit. In fact, the icosahedral structure is best described as a capsid of twelve pentamers. Despite this noticeable difference, the active sites are virtually identical in all structurally studied members. Furthermore, the main regions involved in the catalysis are located at the interface between adjacent subunits in the pentamer. Thus, the two quaternary forms of the enzyme must meet similar structural requirements to achieve their function, but, at the same time, they should differ in the sequence traits responsible for the different quaternary structures observed. Here, we present a combined analysis that includes sequence-structure and evolutionary studies to find the sequence determinants of the different quaternary assemblies of this enzyme. A data set containing 86 sequences of the lumazine synthase family was recovered by sequence similarity searches. Seven of them had resolved three-dimensional structures. A subsequent phylogenetic reconstruction by maximum parsimony (MP) allowed division of the total set into two clusters in accord with their quaternary structure. The comparison between the patterns of three-dimensional contacts derived from the known three-dimensional structures and variation in sequence conservation revealed a significant shift in structural constraints of certain positions. Also, to explore the changes in functional constraints between the two groups, site-specific evolutionary rate shifts were analyzed. We found that the positions involved in icosahedral contacts suffer a larger increase in constraints than the rest. We found eight sequence sites that would be the most important icosahedral sequence determinants. We discuss our results and compare them with previous work. These findings should contribute to refinement of the current structural data, to the design of assays that explore the role of these positions, to the structural characterization of new sequences, and to initiation of a study of the underlying evolutionary mechanisms.Fil: Fornasari, Maria Silvina. Universidad Nacional de Quilmes; ArgentinaFil: Laplagne, Diego Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Frankel, Nicolás. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisiología, Biología Molecular y Celular. Laboratorio de Fisiología y Biología Molecular; ArgentinaFil: Cauerhff, Ana A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Goldbaum, Fernando Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Echave, Julián. Universidad Nacional de Quilmes; Argentin

Fast-Perisomatic sIPSCs

<div><p>(A) and (B) Example of traces of inward sIPSCs recorded from a pup (A) and adult (B) DGC. Dashed box on each top trace denotes expanded segment on the bottom. Scale bars indicate 1 s/50 ms (top/bottom), 40 pA.</p> <p>(C) and (D) Two-dimensional histograms of rise and decay time of individual sIPSCs recorded from pup ([C] <i>n</i> = 5,871 events) and adult DGCs ([D] <i>n</i> = 8,183 events). Color scale indicates the relative frequency for each bin (square areas in the graph).</p> <p>(E) Cumulative histograms of rise and decay time of all sIPSCs recorded from pup (green) and adult (red) DGCs. Data are the same as shown in (C) and (D).</p> <p>(F) Frequency of sIPSCs (pup, <i>n</i> = 12 neurons; adult, <i>n</i> = 15; <i>p</i> = 0.99; <i>t</i>-test).</p> <p>(G) Peak amplitude of sIPSCs (<i>n</i>, same as in [F]; <i>p</i> = 0.44).</p> <p>(H) Kinetics of sIPSCs. Inset: scaled averages of sIPSCs (pup, green; adult, red). Scale bar indicates 10 ms. All experiments conducted in the presence of kyn at V_hold = −80 mV with an internal solution containing high [Cl⁻]. (<i>n</i>, same as in [F]; rise time, <i>p</i> = 0.96; decay time, <i>p</i> = 0.72).</p></div

Fluorescent Labeling of DGCs Born during Early Postnatal and Adult Neurogenesis

<div><p>(A) and (B) Retroviral delivery of GFP into DGCs generated at P7 (A) and P42 (B), analyzed 7 wk after each injection. The GCL was labeled by immunohistochemistry for the neuronal marker NeuN (blue). Images are merges of 27 (A) and 21 (B) confocal planes taken from coronal sections (40-μm thick). H, hilus; ML, molecular layer.</p> <p>(C) and (D) Double retroviral labeling of DGCs generated at P7 (GFP⁺, green) and P42 (RFP⁺, red). Images are merges of nine (C) and 20 (D) confocal planes taken from fixed transverse sections of the DG (400-μm thick) from 13-wk-old mice.</p> <p>(E) Double labeling of DGCs with GFP (green) and BrdU (red): intrahippocampal injections of CAG-GFP retrovirus in P7 were followed by daily injections of BrdU carried out from P21 to P25; brains were analyzed at P53. The image is a merge of 16 confocal planes.</p> <p>(F) Example of a sporadic event of co-localization of GFP, BrdU, and NeuN shown by a single optical section for the green, red, and blue channels. Their overlay is shown together with the orthogonal projections onto the <i>x-z</i> (top) and <i>y-z</i> (right) planes.</p> <p>(G) Number of GFP⁺ or BrdU⁺ cells per mouse (left) and the percentage of GFP⁺ cells showing BrdU label (right). Data are mean ± standard error of the mean (SEM) (<i>n</i> = 3 mice). Scale bars indicate 50 μm (A–E) or 10 μm (F).</p></div

Slow-Dendritic sIPSCs

<div><p>(A) and (B) Example of traces of outward sIPSCs recorded from a pup (A) and adult (B) DGC. Dashed box on each top trace denotes expanded segment on the bottom. Scales indicate 0.5 s/50 ms (top/bottom), 10 pA.</p> <p>(C) and (D) Two-dimensional histograms of rise and decay time of individual sIPSCs recorded from pup ([C] <i>n</i> = 695 events) and adult DGCs ([D] <i>n</i> = 1,160 events). Color scale indicates the relative frequency for each bin.</p> <p>(E) Cumulative histograms of rise and decay time of all sIPSCs recorded from pup (green) and adult DGCs (red). Same data as shown in (C) and (D).</p> <p>(F) Frequency of sIPSCs (pup, <i>n</i> = 10 neurons; adult, <i>n</i> = 16; <i>p</i> = 0.94; <i>t</i>-test).</p> <p>(G) Peak amplitude of sIPSCs (pup, <i>n</i> = 10; adult, <i>n</i> = 14; <i>p</i> = 0.44).</p> <p>(H) Kinetics of sIPSCs. Inset: scaled averages of sIPSCs (pup, green; adult, red). Scale bar indicates 50 ms. All experiments conducted in the presence of kyn at V_hold = 0 mV with an internal solution containing high [Cl⁻]. (<i>n</i>, same as in [F]; rise time, <i>p</i> = 0.37; decay time, <i>p</i> = 0.41).</p></div

Firing Behavior Elicited by Excitatory Inputs

<div><p>(A) Action currents in cell-attached configuration recorded from an adult-born DGC in response to MPP stimulation at increasing stimulus strengths (0.5–1.5 mA, 50 μs). Six representative epochs are shown. Spiking probability (p) is shown below the traces. The asterisk (*) marks the stimulation artifact. Scale indicates 10 ms, 50 pA.</p> <p>(B) Sample experiment of simultaneous cell-attached recordings of DGCs born in pup and adult brain in response to MPP stimulation (0.4 mA, 50 μs). Action currents indicate a higher spiking probability in the pup DGC. Scales indicate 10 ms, 50 pA (left) and 20 pA (right).</p> <p>(C) Sample experiment in which the spiking probability is higher in the adult-born DGC (1.5 mA, 50 μs). Scale indicates 10 ms, 30 pA.</p> <p>(D) Firing behavior of DGCs born in pup and adult brain during simultaneous paired experiments. No significant difference was found (<i>n</i> = 14 pairs, <i>p</i> = 0.8, Wilcoxon signed rank test). All recordings were carried out in the presence of BMI (20 μM). In this set of experiments, adult-born neurons were retrovirally labeled with GFP, whereas unlabeled DGCs of the middle third of the GCL were considered postnatally born (see <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0040409#s4" target="_blank">Materials and Methods</a>). Repetitive (>15 episodes) slow frequency stimulation was used to measure the spiking probability for each neuron at the given stimulus.</p></div

Short-Term Plasticity of Entorhinal Glutamatergic Afferents

<div><p>(A) Average EPSCs recorded at V_Hold = −80 mV (downward deflections) and +50 mV (upward deflections) from pup and adult DGCs (<i>n</i> = 8 to 11) upon stimulation of MPP or LPP. Dashed line indicates zero level. Arrowheads denote time points for quantification of AMPA (open triangles) and NMDA (filled triangles) currents shown in (B). Criteria for AMPA/NMDA quantification are detailed in the <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0040409#s4" target="_blank">Materials and Methods</a> section. Scale bars indicate 20 ms, 100 pA.</p> <p>(B) AMPA/NMDA ratio from pup and adult DGCs (<i>n</i> = 9 to 13) in response to MPP or LPP stimulation. Two-way ANOVA revealed a significant effect of MPP versus LPP (<i>p</i> = 0.006), but no significant effect of pup versus adult (<i>p</i> = 0.63).</p> <p>(C) Averages of EPSCs in response to paired-pulse stimulation of the MPP or LPP delivered at increasing interpulse intervals (20, 50, 100, and 500 ms). Traces are averages of 7–14 cells aligned and normalized to the first EPSC. Stimulation artifacts and late decay phases of the second EPSC were removed for clarity. Scale bar indicates 100 ms.</p> <p>(D) Paired-pulse ratio as a function of interpulse interval for the experiments shown in (C). Two-way ANOVAs revealed a significant effect of interpulse interval for MPP (dashed lines, <i>p</i> < 0.0001) and LPP (solid lines, <i>p</i> < 0.0001), but no significant effect of pup (green lines, solid circles) versus adult (red lines, open circles) for either MPP (<i>p</i> = 0.073) or LPP (<i>p</i> = 0.72) stimulation (<i>n</i> = 9 to 14)</p> <p>(E) Example of EPSCs from a pup (green) and an adult DGC (red) in response to MPP stimulation (ten pulses, 50 Hz) Traces are normalized to the first EPSC amplitude. Scale bar indicates 40 ms.</p> <p>(F) Relative EPSC amplitudes measured in response to 50-Hz stimulation evoked as shown in (E). No difference was found between pup and adult responses (two-way ANOVA, <i>p</i> = 0.49, <i>n</i> = 10 pups [solid circles], <i>n</i> = 4 adults [open circles]). All recordings were carried out in the presence of 20-μm BMI. Neurons were approximately 18 wk old (pup) and approximately 13 wk old (adult). All plots depict mean ± SEM.</p></div